Simplify the following expression: $z = \dfrac{-21y - 30}{-30y + 12}$ You can assume $y \neq 0$.
Explanation: Find the greatest common factor of the numerator and denominator. The numerator can be factored: $-21y - 30 = - (3\cdot7 \cdot y) - (2\cdot3\cdot5)$ The denominator can be factored: $-30y + 12 = - (2\cdot3\cdot5 \cdot y) + (2\cdot2\cdot3)$ The greatest common factor of all the terms is $3$ Factoring out $3$ gives us: $z = \dfrac{(3)(-7y - 10)}{(3)(-10y + 4)}$ Dividing both the numerator and denominator by $3$ gives: $z = \dfrac{-7y - 10}{-10y + 4}$